Electrodynamic actuator



July `1, 1969 P. WILDI 3,453,463

u ELECTRODYNAMIC ACTUATOR Filed Feb. 5. 1968 FIG. l.

23 32 al l le 8 4a FIG. 2. 2

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:a2 2 las l2 J4 42 ,\J\/ENTOR PA U L WIL DI ATTORNEYS United States Patent O 3,453,463 ELECTRODYNAMIC ACTUATOR Paul Wildi, San Diego, Calif., assignor to Gulf General Atomic Incorporated, San Diego, Calif., a corporation of Delaware Filed Feb. 5, 1968, Ser. No. 703,006

Int. Cl. 33/00 U.S. Cl. 310--27 7 Claims ABSTRACT OF THE DISCLOSURE An electromagnetic actuator is described utilizing induced magnetic elds to displace an actuating element. The electromagnetic actuator includes means for damping recoil produced by the repelling forces.

This invention relates to electromagnetic actuators and, more particularly, to angelectromagnetic actuator in which the effect of recoil forces is minimized.

The term electromagnetic actuator, as it is used herein, is intended to refer to a device having a movable actuating element or member which is displaced in response to the production of a very strong electromagnetic eld or fields. The actuating element may be coupled to operate any suitable type of mechanism, such as a switch or circuit breaker, valve, riveter, or hammer.

An electromagnetic actuator may include a coil through which a very high current pulse is passed to produce a strong electromagnetic field. The actuating element has at least a portion thereof constructed of conductive material positioned proximate the coil. When a current pulse flows through the coil to produce a transient magnetic field, current is induced in the conductive portion of the actuating element causing an interaction between the induced current and the magnetic field thereby producing a repulsion force between the coil and actuating element which varies with the intensity of the magnetic field. Accordingly, the actuating element and the coil are strongly and suddenly repelled with respect to each other, producing displacement of the actuating element to perform the desired function.

Electromagnetic actuators generally constructed as described may be satisfactory for many purposes. For some applications, however, such as hand held electromagnetic actuators (e.g. automatic hammers and rivetters), the recoil of the coil produced from operation of the actuating element may be intolerable. For example, excessive recoil may render an electromagnetic autuator difficult or impossible to hand hold. If recoil is absorbed by making the coil movable, and by damping such movement, electrical leads and coolant connections for the coil may be subject to excessive wear.

Accordingly, it is an object of this invention to provide an improved electromagnetic actuator.

Another object of the invention is to provide an electromagnetic actuator of improved construction wherein recoil forces are effectively absorbed.

A further object of the invention is to provide an electromagnetic actuator wherein recoil forces are effectively absorbed without subjecting electrical leads and coolant conductors to excessive wear.

Other objects of the invention will become apparent to those skilled in the art from the following description taken in connection with the accompanying drawings wherein:

FIGURE l is a full section side view of a particular type of electromagnetic actuator constructed in accordance with the invention; and

FIGURE 2 is a full section side view of an alternative embodiment of the invention.

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Very generally, the electromagnetic actuator of the invention comprises a primary coil 11 and means 12 for supporting same. Also included is a secondary coil 13 and means 14 for supporting the secondary coil so that it is movable with respect to the primary coil. The secondary coil is positioned sufficiently close to the primary coil that a current is induced in the secondary coil upon energization of the primary coil. An actuating element 16 has a conductive portion 17 positioned sufficiently close to the secondary coil to be repelled with respect to the secondary coil upon energization of the primary coil. A damping device 18 is provided for damping movement of the secondary coil.

Referring now more particularly to FIGURE 1, the electromagnetic actuator illustrated therein constitutes an electromagnetic hammer which may be utilized for driving nails. The hammer includes an outer housing consisting of a generally cylindrical main section 21 closed at one end and a generally -frusto conical front cover section 22 bolted at its base to the other end of the main section at mating flanges 23. A handle 24 is cost integral with the main section of the housing at the one end thereof. The main section of the housing is provided with a boss 26 to which a suitable handle 27 is attached. An opening 28 is provided in the closed end of the main section of the housing axially thereof for purposes which will be explained below. Similarly, an axial opening 29 is provided centrally of the front cover section 22 of the housing 4for purposes which are also explained below.

The primary coil 11 is disposed within the main section 21 and consists of a plurality of turns wound upon a supporting core 12 of conductive material having a helical groove 31 in its outer surface for accommodating the coil turns. The supporting core is provided with a gap or slit (not shown) so that the core does not act as a shorted turn. The primary coil support means or core 12 is embedded in an annular liner 32 of a suitable insulating material such as epoxy. The liner 32 is secured to the interior surface of the housing 21-22 to be supported thereby. Accordingly the coil 11 is supported in fixed relation to the housing. Electrical connections, not illustrated, for the coil 11 are connected to one end of a cable 33 which passes through a suitable passage, not illustrated, within the handle 27. Flexible conduits for passing coolant through the liner 32 in order to cool the coil 11 may also be provided in the cable 33. A trigger 35 is provided in the handle 27 to initiate operation of the electromagnetic hammer as described below.

As shown in FIGURE 1, the secondary coil 13 is disposed within the space defined by the Supporting core 12 and consists of a hollow cylinder of conductive material having a portion 34 of increased thickness toward the front end thereof. The secondary coil is provided with a gap or slit 36, which may fbe open or filled with a suitable insulating material, so that the secondary coil does not constitute a shorted turn. The rear end of the secondary coil 13 is disposed in an annular recess 37 at the periphery of a disk 38 of insulating material which is supported by the damping device 18, as hereinafter described.

The actuating element 16 is disposed at the front end of the secondary coil 13 coaxially therewith and it has an approximately frusto conical front surface. Its rear surface is provided with an axial recess 41 in order that its mass will be substantially less than the mass of the secondary coil 13, the reason bein-g explained below. The conductive portion 17 of the actuating element 16 is a. generally annular strip surrounding the recess 41 and lying in a plane perpendicular to the axis of the actuating element 16. A layer 42 of insulating material is disposed on the secondary coil 13 facing the strip 17. A cylindrical hammer portion 43 extends along the axis of the actuating element 16 and projects through the opening 29 in the front section 22. The tip of the hammer portion 43 is provided with a recess 44 therein in which -a nail head may be captured. This facilitates alignment of the electromagnetic actuator with the nail and aids in driving the nail.

A coil spring 46 extends from the rear end of the housing 21-22 to the disk 38 and is maintained under compression to bias the disk 38 against the rear end of the secondary coil 13 (towards the left in FIGURE 1). A second coil spring 47 extends from an annular recess 48 in the front section 22 of the housing to engage the front surface of the actuating element 16. The spring 47 is maintained under compression to bias the actuating e1ement against the secondary coil 13 at the widened portion 34' thereof. Electrical separation is maintained by the insulation layer 42. The bias of the spring 46 is stronger than the bias of the spring 47 so that the normal position of the elements of the electromagnetic actuator will Ibe as shown in FIGURE 1 when the primary coil 11 is not energized.

In order to damp movement of the secondary coil 13 when the device is operated, the damping means 18 is provided. Such damping means includes the coil spring 46 and also includes a dash-pot comprising a fluid filled cylinder 51, a piston 52, and a piston rod 53 coupling the piston 52 to the disc 38. The cylinder 51 is supported in the opening 28 of the housing main section 21.

When the electromagnetic actuator of FIGURE 1 is to lbe operated, a pulse of current is applied to the primary coil 11. Thi-s pulse of current may be derived from any suitable source. For example, a satisfactory pulse circuit, not illustrated, may include a capacitor bank charged Iby suitable high voltage rectifier circuit and which is suddenly discharged through a switch, such as a battery of ignitrons.

Energization of the primary coil 11 through application of a high current pulse thereto produce a very strong transient magnetic field. This magnetic field is shaped by the secondary coil due to the current induced in the secondary coil by the field produced by the primary coil. The resulting magnetic field has lines of force which pass through the hollow center of the secondary coil 13 and surround both the secondary coil and primary coil as illustrated by the dotted line 56 in the drawing.

The .field produced by the secondary coil induces current in the conductive portion 17 of the actuating element 16, which is immediately adjacent the secondary coil 13. The interaction Ibetween the induced current and the magnetic field subjects the secondary coil and the actuating element to a repulsion force varying with the intensity of the magnetic field. The actuating element and the secondary coil are therefore strongly repelled with respect to each other, the actuating element tending to move to the left in the FIGURE 1 and the secondary coil 13 tending to move to the right in FIGURE 1. The foregoing action drives the hammer portion 43 of the device against the nail disposed in the recess 44 to drive the nail.

Because the mass of the actuating element 16 is substantially less than the mass of the secondary coil 13, the kinetic energy imparted to the actuating element is greater (the Ikinetic energy imparted to the two bodies ibeing inversely proportioned to their respective masses). This enhances efficiency and affords some reduction in the recoil which must be absorbed by the remainder of the electromagnetic actuator.

The kinetic energy which is imparted to the secondary coil 13 as a result of the current pulse in the primary coil 11 drives the secondary coil to the right in FIGURE 1. This energy is absorbed by the damping means 18 consisting of the spring 46 and the dash-pot 51-52. The energy which is imparted to the housing 21-22, and hence the energy which the operator holding the electromagnetic actuator must contend with, is minimal. After the energy is absorbed, the 'bias of the spring 46 returns the device to the illustrated position, against the bias of the spring 47 and the drag on the dash-pot piston 52. Since no axial force is imparted to the coil 11, no force operates directly upon the housing 21422, making it easy for the operator to hold the device.

Referring now to FIGURE 2, an alternative embodi ment of the invention is illustrated. The device illustrated in FIGURE 2 is also an electromagnetic hammer and elements thereof substantially identical in function to those elements in the embodiment of FIGURE l are given identical reference numerals preceded by a l.

In the embodiment of FIGURE 2, the primary or stationary coil 111, although coaxial with the secondary or movable coil 113, is positioned inside of the secondary coil. The insulation material or liner 132 is of a different configuration from t-hat in the embodiment of FIGURE 1, consisting Igenerally of a cylindrical support projecting axially in the housing 121-122. The secondary coil 113 is able to slide axially back and forth upon operation of the device to drive the actuating element 116. Recoil forces on the secondary coil 113 are absorbed by the absorbing means 118 which, in the embodiment of FIGURE 2, consist of only a coil spring 146. If desired, however, a suitable energy absorbing means, such as a dash-pot, may be incorporated in the device.

Although described herein in connection with electromagnetic hammers, the invention is not so limited, nor is it limited to hand held tools. Thus, the invention may be used in connection with stationary arrangements where it becomes desirable to minimize recoil of an electromagnetic actuator. As previously mentioned, such applications may be in the actaution of valves, switches, etc.

It may therefore :be seen that the invention provides an improved electromagnetic actuator in which recoil is minimized. Because the primary coil 11 or 111 is stationary relative to the housing, excessive wear and tear on electrical leads or coolant conduits is avoided. Moreover, construction of coils generally of the illustrated configuration facilitates manufacture and enhances operational life expectancy.

Various modifications of the invention in -addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Such modifications are intended to fall within the scope of the appended claims.

What is claimed is:

1. An electromagnetic actuator comprising, -a primary coil, means for supporting said primary coil, a secondary coil, -means for supporting said secondary coil for movement relative to said primary coil, said secondary coil being in inductive relation to said primary coil, an actuating element having a conductive portion positioned in inductive relation to said secondary coil whereby said actuating element is repelled with respect to said secondary coil upon energization of said primary coil, and means coupled to said secondary coil support means for damping movement of said secondary coil. 2. An electromagnetic actuator according to claim 1 including a housing, and wherein said primary coil supportln-g means secures said primary coil in a fixed position with respect to said housing.

3. An electromagnetic actuator according to claim 1 wherein said primary coil and said secondary coil are coaxial.

4. An electromagnetic actuator according to claim 3 wherein said secondary coil is positioned within said primary coil, and wherein said actuating element is axially aligned with said secondary coil and is of less mass than said secondary coil.

5. An electromagnetic actuator according to claim 3 wherein said primary coil is positioned within said secondary coil, and wherein said actuating element is axially aligned with said secondary coil.

6. An electromagnetic actuator according to claim 1 wherein said secondary coil and said actuating element are resiliently biased toward each other.

7. An electromagnetic actuator according to claim 6 FOREIGN PATENTS wherein said damping means comprise a dash-pot. 655,122 1/1963 Canada- 1,272,951 8/ 1961 France. References Cited 1,009,714 3/ 1952 France,

r" 67 366 [Jb/T? TATS PATENTS 3 L) MILTON O. HIRSHFIELD, Primary Examiner. 1,1 1 9 essen en 10-15 2,645,728 7/1953 Willson eral 31u-27 D' F DUGGANAmsmntEmmne" 2,820,161 1/1958 Lewis 31027 US. CL R- 3,161,793 12/1964 Laithwaite 310-27 10 173 117 

